CN114152592A - Method and apparatus for determining a reflectivity value indicative of the reflectivity of an object - Google Patents
Method and apparatus for determining a reflectivity value indicative of the reflectivity of an object Download PDFInfo
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- G01S17/88—Lidar systems specially adapted for specific applications
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- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
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- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
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Abstract
Embodiments of the present disclosure relate to methods and apparatus for determining a reflectivity value indicative of the reflectivity of an object. A method for determining a reflectivity value indicative of the reflectivity of an object is provided. The method includes performing a time-of-flight (ToF) measurement using a ToF sensor. The correlation function of the ToF measurement increases with distance within the measurement range of the ToF sensor, so that the output value of the ToF sensor used for the ToF measurement is independent of the distance between the ToF sensor object and the object. The method also includes determining a reflectance value based on an output value of the ToF sensor for the ToF measurement.
Description
Technical Field
The present disclosure relates to reflectance sensing. In particular, examples relate to methods and apparatus for determining a reflectance value indicative of a reflectance of an object using a time-of-flight (ToF) sensor.
Background
Two-dimensional imaging using ToF cameras is used for object detection and classification (e.g., facial recognition, production, intelligent monitoring, etc.).
If the scene is illuminated by a light source close to the light capturing section, the measured light intensity depends on the distance to the object according to the inverse square law of a point light source. This prevents measuring the actual reflectivity of the object, which is important information for object identification. Furthermore, objects in the near vicinity reflect too much light, which can lead to saturation at the ToF camera. Furthermore, if the light source is located close to the light capturing portion, close objects (e.g. cover glass or organic light emitting diode OLED displays) may cause stray light to enter the light capturing portion.
Thus, there may be a need for improved reflectance sensing using ToF sensors.
Disclosure of Invention
This requirement may be met by the subject matter of the appended claims.
One example relates to a method for determining a reflectivity value indicative of a reflectivity of an object. The method includes performing a ToF measurement using a ToF sensor. The correlation function of the ToF measurement increases with distance within the measurement range of the ToF sensor, so that the output value of the ToF sensor used for the ToF measurement is independent of the distance between the ToF sensor and the object. The method also includes determining a reflectance value based on an output value of the ToF sensor for the ToF measurement.
Another example relates to an apparatus for determining a value indicative of a reflectivity of an object. The apparatus includes a ToF sensor configured to perform ToF measurements. The correlation function of the ToF measurement increases with distance within the measurement range of the ToF sensor, so that the output value of the ToF sensor used for the ToF measurement is independent of the distance between the ToF sensor and the object. The apparatus also includes a processing circuit configured to determine a reflectance value based on an output value of the ToF sensor for ToF measurement.
Drawings
Some examples of the apparatus and/or methods will now be described, by way of example only, with reference to the accompanying drawings, in which
FIG. 1 shows a flow chart of an example of a method for determining a reflectance value;
FIG. 2 shows an example of an apparatus for determining reflectance values; and
fig. 3 shows an exemplary process of a correlation function of the ToF sensor, an output value of the ToF sensor, and a light intensity of light received at the ToF sensor with distance.
Detailed Description
Some examples are now described in more detail with reference to the accompanying drawings. However, other possible examples are not limited to the features of the embodiments described in detail. Other examples may include modifications of the feature and equivalents and alternatives to the feature. Furthermore, the terminology used herein to describe certain examples should not be limiting of other possible examples.
Throughout the description of the figures, the same or similar reference numerals refer to the same or similar elements and/or features, which may be implemented in the same or modified forms while providing the same or similar functions. The thickness of lines, layers and/or regions in the figures may also be exaggerated for clarity.
When two elements a and B are used in "or" combination, this should be understood as disclosing all possible combinations, i.e. only a, only B and a and B, unless explicitly defined otherwise in individual cases. As an alternative wording to the same combination, "at least one of a and B" or "a and/or B" may be used. The same applies to combinations of more than two elements.
Further examples may also use multiple elements to achieve the same functionality if singular forms are used, such as "a", "an", and "the", and the use of only a single element is not explicitly or implicitly defined as mandatory. If a function is described below as being implemented using multiple elements, further examples may implement the same function using a single element or a single processing entity. It will be further understood that the terms "comprises," "comprising," "includes" and/or "including," when used, specify the presence of stated features, integers, steps, operations, procedures, elements, components, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, procedures, elements, components, and/or groups thereof.
Fig. 1 shows a flow chart of an example of a method 100 for determining a reflectivity value indicative of the reflectivity of an object. The method 100 will be described further below with reference to fig. 2, which fig. 2 shows an exemplary apparatus 200 for determining a reflectivity value indicative of the reflectivity of an object 201.
The illumination element 230 generates modulated light 203. The illumination element 230 may include any number of light sources. The illumination element 230 may, for example, include one or more Light Emitting Diodes (LEDs) and/or one or more laser diodes (e.g., one or more vertical cavity surface emitting lasers VCSELs) that are excited based on an illumination signal.
The light capturing element 220 may include various components, such as optics (e.g., one or more lenses) and electronic circuitry. In particular, the electronic circuit arrangement comprises an image sensor comprising at least one light sensitive element or pixel (e.g. comprising a photonic mixer device PMD or a charge coupled device CCD). For example, an image sensor may include a plurality of photosensitive elements or pixels. At least one light sensitive element or pixel is driven based on a reference signal.
The method 100 includes performing 102 a ToF measurement using the ToF sensor 210. The parameters of ToF sensor 210 are adjusted such that the correlation function (sensor response function) of ToF sensor 210 used for ToF measurement increases with distance (e.g., strictly monotonous) within the measurement range of ToF sensor 210, so that the output value of ToF sensor 210 used for ToF measurement is independent of the distance between ToF sensor 210 and object 201.
Assuming that the light intensity (intensity) of the light 203 received at the ToF sensor 210 during the ToF measurement is constant with distance over the measurement range of the ToF sensor 210, the correlation function represents the expected distance-dependent output of the ToF sensor 210 for the ToF measurement. This is shown in fig. 3. The abscissa of fig. 3 represents the distance between ToF sensor 210 and object 201. In the example of fig. 3, it is assumed that the distance of the entire abscissa is within the measurement range of the ToF sensor 210. The ordinate represents the output of the ToF sensor 210. An exemplary process 310 of correlation function over distance is shown in fig. 3. As can be seen from exemplary process 310, the correlation function of the ToF measurement increases with distance (i.e., the greater the distance between ToF sensor 210 and object 201, the greater the correlation function).
For the correlation function of the ToF measurement, it is assumed that the light intensity of the light received at the ToF sensor 210 during the ToF measurement is constant. Referring to the example of fig. 2, it is assumed (regardless of the distance between ToF sensor 210 and object 201) that the light intensity of light 203 reflected by object 201 back to light capturing element 220 is substantially constant.
However, the light intensity of the light 203 received by the light capturing element 220 actually depends on the distance between the ToF sensor 210 and the object 201. Specifically, the light intensity of the light 203 received by the light capturing element 220 decreases as the distance between the ToF sensor 210 and the object 201 increases. This is further illustrated in fig. 3. Fig. 3 shows an exemplary process 330 of light intensity of light 203 received at ToF sensor 210 over distance (the ordinate of fig. 3 further indicates light intensity). As can be seen from process 330, the light intensity decreases with distance. For example, it may be assumed that the light intensity decreases according to the inverse square law. That is, the distance-dependent light intensity of the light 203 received at the ToF sensor 210 can be assumed as follows:
i represents the light intensity of light received at ToF sensor 210 and d represents the distance between ToF sensor 210 and object 201 reflecting light 203 back to ToF sensor 210.
Thus, adjusting the ToF sensor 210 such that the correlation function of the ToF sensor 210 for ToF measurements increases with distance within the measurement range of the ToF sensor 210 allows compensating for a decrease in the light intensity of the light 203 received at the ToF sensor 210. For example, the process 310 of correlation function versus distance may be adjusted to be the inverse of the process 330 of light intensity versus distance of the light 203 received at the ToF sensor 210. The distance-dependent correlation function c (d) can be set, for example, as follows:
c(d)∝d2 (2)
as a result, the output value of ToF sensor 210 used for ToF measurement is independent of the distance between ToF sensor 210 and object 201. This is further illustrated in fig. 3, which fig. 3 illustrates an exemplary process 320 of output values of ToF sensor 210.
The output value of ToF sensor 210 is proportional to the reflectivity of object 201, since the reflectivity of object 201 determines how much light reaches ToF sensor 210 during ToF measurements. Therefore, the output value of ToF sensor 210 varies with the reflectivity of object 201 — regardless of the distance between ToF sensor 210 and the object. Thus, when the correlation function is used for ToF measurement as described above, the output value of ToF sensor 210 allows characterizing the reflectivity of object 201.
Referring again to fig. 1, method 100 further includes determining 104 a reflectance value indicative of a reflectance of object 201 based on an output value of ToF sensor 210 for ToF measurement. For example, determining 104 a reflectance value may include applying at least one correction to an output value of ToF sensor 210 for ToF measurements. The output value of ToF sensor 210 for ToF measurements may be scaled and/or offset corrected, for example, to obtain a reflectance value. Accordingly, a systematic error (e.g., noise) can be corrected.
For example, the processing circuit 240 may also output data (e.g., a two-dimensional image) indicative of reflectance values.
The apparatus 200 may include additional hardware, conventional and/or custom.
In other words, a two-dimensional sensing method based on a ToF camera is proposed. The result of the sensing may be, for example, a two-dimensional image in which pixels respectively indicate the amount of light reflected by the object. As described above, this can be achieved by using a sensor response function that is close to the inverse of the received light intensity function with distance. Since this makes the sensor output larger with distance, the loss of signal strength is compensated for. This results in a constant sensor output of the object independent of distance.
As described above, to perform 102ToF measurements, the method 100 includes a) illuminating a scene including the object 201 with the modulated light 202 of the illumination element 230 based on an illumination signal, and b) driving the light capturing element 230 based on a reference signal. In order to adjust the correlation function of the ToF measurement such that it increases with distance within the measurement range of the ToF sensor 210, at least one of the illumination signal, the reference signal and the time offset between the illumination signal and the reference signal may be varied during the ToF measurement.
For ToF measurements, Coded Modulation (CM) measurements as well as Continuous Wave (CW) measurements may be used.
For example, if CW measurements are used for ToF measurements, each of the illumination and reference signals exhibits a respective alternating series of high and low pulses of equal duration (length). Thus, the modulated light 202 is a series of light pulses having equal pulse lengths (durations) and equal pulse intervals. To adjust the correlation function of the ToF measurement so that it increases with distance within the measurement range of ToF sensor 210, the time offset between the illumination signal and the reference signal may be varied during the CW measurement.
Alternatively, if CM measurements are used for ToF measurements, at least one of the illumination signal and the reference signal exhibits a respective alternating series of high and low pulses having different durations (lengths). For example, the modulated light 202 may be a series of light pulses having different pulse lengths (lengths) and/or different pulse intervals. Similarly, for CM measurements, the reference signal may exhibit a series of alternating high and low pulses with different durations. In other examples, the modulated light 202 may be a series of light pulses with equal pulse length and equal pulse spacing, while the reference signal exhibits a series of alternating high and low pulses with different durations. To adjust the correlation function of the ToF measurement such that it increases with distance within the measurement range of the ToF sensor 210, the corresponding series of alternating high and low pulses may be varied for at least one of the illumination signal and the reference signal during the CM measurement. Alternatively or additionally, the time offset between the illumination signal and the reference signal may be changed during CM measurements.
By varying one or more of the illumination signal, the reference signal, and the time offset between the illumination signal and the reference signal during ToF measurement, ToF sensor 210 may create a variety of different secondary correlation functions. Regardless of whether CW or CM measurements are performed, ToF sensor 210 temporarily exhibits a respective secondary correlation function for each variation of the illumination signal, the reference signal, and the time offset between the illumination signal and the reference signal used during ToF measurements. The resulting (overall) correlation function of the ToF measurement may be understood as a combination (e.g. sum) of different auxiliary correlation functions used during the ToF measurement. In other words, the resulting (effective) correlation function of ToF sensor 210 used for ToF measurements is a combination of the illumination signal, the reference signal and the varying auxiliary correlation function of the temporal offset between the illumination signal and the reference signal used during ToF measurements. For example, by switching the secondary correlation functions within the exposure time of the ToF measurement, a weighted sum of the different secondary correlation functions (i.e. the different sensor response functions) may be obtained as the correlation function of the ToF measurement. Thus, a correlation function of the custom shape of ToF sensor 210 for ToF measurements may be acquired/adjusted.
For example, to obtain a correlation function for ToF measurements that increase with distance within the measurement range of ToF sensor 210, at least one of the illumination signal, the reference signal, and the time offset between the illumination signal and the reference signal may be varied such that the secondary correlation functions are offset relative to each other (e.g., offset along the abscissa in fig. 3) within the measurement range of the ToF sensor. For example, to create a correlation function that increases with distance within the measurement range of ToF sensor 210, an auxiliary CM correlation function having one correlation peak may be continuously shifted during exposure.
Alternatively, the speed of the shift may be modulated such that different shifts of the auxiliary CM correlation function are weighted differently in the resulting correlation function. For example, during CM measurements, for at least one of the illumination signal and the reference signal, the corresponding series of alternating high and low pulses may be varied with increasing rate of change. For example, if one of the illumination signal and the reference signal is changed by successively selecting different ones of a plurality of (pool) codes for generating a respective one of the illumination signal and the reference signal, the selection or update rate/frequency may be increased during CM measurements. Similarly, during CM measurements, the time offset between the illumination signal and the reference signal may change as the rate of change increases.
By varying the rate of change, the offset between the resulting secondary correlation functions can be modulated such that the secondary correlation functions are weighted differently in the overall correlation function used for ToF measurements.
Within the measurement range, the course of the correlation function over distance of the ToF measurement may for example depend on the course of an estimate over distance of the actual light intensity of the light 203 received at the ToF sensor 210. For example, an estimated course over distance of the actual light intensity of the light 203 received at the ToF sensor 210 may be obtained in a factory calibration. Thus, the correlation function of the ToF measurement can be (pre-) determined in a factory calibration. For example, the illumination signal, the reference signal, and the variation in the time offset between the illumination signal and the reference signal used during ToF measurement may be selected/adjusted based on factory calibration.
Alternatively or additionally, the correlation function of the ToF measurement may be adapted/adjusted on the fly (e.g. to correct errors such as distance dependent errors). For example, method 100 may include performing a plurality of ToF calibration measurements with ToF sensor 210 to acquire calibration data indicative of actual light intensities of light 203 received at ToF sensor 210 for different distances between ToF sensor 210 and reference object 201. Thus, the calibration data is an estimate of the course of the actual light intensity of the light 203 received at the ToF sensor 210. Thus, the correlation function (for) ToF measurement may be adjusted based on the calibration data. For example, the variations of the illumination signal, the reference signal and the time offset between the illumination signal and the reference signal used during ToF measurement may be adapted (adjusted) based on the calibration data.
Further, a constant output value of the ToF sensor may be obtained taking into account a drift of an operating parameter of the lighting element 220. For example, the generation of the illumination signal and the operation of the driver electronics in the illumination element 220 are temperature dependent. Accordingly, the method 100 may include measuring a temperature at the lighting element 220. The apparatus 200 may include one or more temperature sensors for measuring the temperature at the lighting element 220. Alternatively or additionally, the method 100 may comprise measuring the light intensity and/or the rise time of the modulated light 202 emitted by the lighting element 220. The apparatus 200 may comprise one or more light sensors (e.g. photodiodes) for measuring the light intensity and/or the rise time of the modulated light 202 emitted by the lighting element 220. Based on at least one of the measured temperature at the lighting element 220 and the measured light intensity and/or rise time of the modulated light 202 emitted by the lighting element 220, the illumination signal, the reference signal and the time offset between the illumination signal and the reference signal may be varied to compensate for temperature dependent drift in the operation of the lighting element 220.
According to an example, the reflectivity sensing described above may be used with depth sensing to provide depth and reflectivity data (e.g., depth and reflectivity images). For example, method 100 may also include performing one or more additional ToF measurements using ToF sensor 210. Accordingly, a distance value indicative of the distance of ToF sensor 210 to object 201 may be determined based on the output of ToF sensor 210 for one or more additional ToF measurements. Further, data indicative of the reflectance value and the distance value may be output. For example, one or more images indicative of reflectance values and distance values may be output.
In other examples, the correlation function increases with distance within the measurement range of ToF sensor 210, but does not match the assumption/estimation process of the light intensity of light 203 received at ToF sensor 210. In other words, the correlation function does not satisfy the above mathematical expression (2). Adjusting the correlation function may enable High Dynamic Range (HDR) imaging.
Examples as described herein may be summarized as follows:
some examples relate to a method for determining a reflectivity value indicative of a reflectivity of an object. The method includes performing a ToF measurement using a ToF sensor. The correlation function of the ToF measurement increases with distance within the measurement range of the ToF sensor, so that the output value of the ToF sensor used for the ToF measurement is independent of the distance between the ToF sensor and the object. The method also includes determining a reflectance value based on an output value of the ToF sensor for the ToF measurement.
According to some examples, assuming that the light intensity of light received at the ToF sensor during ToF measurement is constant over distance within the measurement range of the ToF sensor, the correlation function represents an expected distance-dependent output of the ToF sensor for the ToF measurement.
In some examples, determining the reflectance value includes: at least one correction is applied to the output value of the ToF sensor used for ToF measurements.
According to some examples, performing ToF measurements comprises: illuminating a scene comprising an object with modulated light based on an illumination signal; driving a light capturing element of the ToF sensor based on the reference signal; and varying at least one of the illumination signal, the reference signal, and a time offset between the illumination signal and the reference signal during the ToF measurement.
In some examples, each of the illumination signal and the reference signal exhibits a respective alternating series of high and low pulses of equal duration, with the time offset between the illumination signal and the reference signal varying during the ToF measurement.
In an alternative example, at least one of the illumination signal and the reference signal exhibits a respective alternating series of high-low pulses having different durations, wherein the respective alternating series of high-low pulses is varied for at least one of the illumination signal and the reference signal during the ToF measurement.
According to some examples, the respective alternating series of high and low pulses varies at an increasing rate of variation for at least one of the illumination signal and the reference signal during the ToF measurement.
In some examples, the time offset between the illumination signal and the reference signal is varied during the ToF measurement.
According to some examples, the ToF sensor temporarily exhibits a respective auxiliary correlation function for each variation of the illumination signal, the reference signal and the time offset between the illumination signal and the reference signal used during the ToF measurement, wherein the correlation function of the ToF measurement is a combination of the auxiliary correlation functions, and wherein at least one of the illumination signal, the reference signal and the time offset between the illumination signal and the reference signal is varied such that the auxiliary correlation functions are offset relative to each other within the measurement range of the ToF sensor.
In some examples, the modulated light is emitted by an illumination element of the ToF sensor, and the method further comprises: measuring a temperature at the lighting element; and/or measuring the light intensity and/or the rise time of the modulated light emitted by the lighting element; and varying at least one of the illumination signal, the reference signal and a time offset between the illumination signal and the reference signal based on at least one of the measured temperature at the illumination element and the measured light intensity and/or rise time of the modulated light emitted by the illumination element.
According to some examples, the course of the correlation function over distance of the ToF measurement depends on the estimated course of the actual light intensity of the light received at the ToF sensor over distance in the measurement range.
In some examples, the correlation function in which ToF measurements are made is predetermined in a factory calibration.
According to some examples, the method further comprises: performing a plurality of ToF calibration measurements to acquire calibration data indicative of actual light intensity of light received at the ToF sensor for different distances between the ToF sensor and a reference object; and adjusting a correlation function of the ToF measurement based on the calibration data.
In some examples, the method further comprises: performing one or more additional ToF measurements using the ToF sensor; determining a distance value indicative of a distance to the object based on an output of the ToF sensor for one or more further ToF measurements; and outputting data indicative of the reflectance value and the distance value.
Other examples relate to an apparatus for determining a value indicative of a reflectivity of an object. The apparatus includes a ToF sensor configured to perform ToF measurements. The correlation function of the ToF measurement increases with distance within the measurement range of the ToF sensor, so that the output value of the ToF sensor used for the ToF measurement is independent of the distance between the ToF sensor and the object. The apparatus also includes a processing circuit configured to determine a reflectance value based on an output value of the ToF sensor for ToF measurement.
Examples of the present disclosure may enable depth independent intensity imaging using a ToF camera. Examples of the present disclosure introduce a ToF modulation mode that can provide a two-dimensional image in which pixel values depend on object reflectivity — independent of distance. In other words, the ToF camera operates in a mode in which the sensor output of the object is uniform within the measurement range. This may be useful for example for surveillance and face recognition, since for these applications two-dimensional images carry more information than depth images. The reflectivity image contains even more information.
Aspects and features described in relation to a particular one of the preceding examples may also be combined with one or more other examples to replace the same or similar features of that other example or to otherwise introduce these features into the other examples.
It should also be understood that the disclosure of several steps, processes, operations, or functions disclosed in the specification or claims should not be construed as implying that such operations are necessarily order dependent, unless explicitly stated otherwise or necessary for technical reasons. Thus, the preceding description does not limit the execution of several steps or functions to a particular order. Further, in further examples, a single step, function, process, or operation may include and/or be broken down into several sub-steps, functions, processes, or operations.
If certain aspects have been described with respect to a device or system, these aspects should also be understood as descriptions of corresponding methods. For example, a block, device, or functional aspect of a device or system may correspond to a feature of a corresponding method, such as a method step. Thus, aspects described with respect to a method should also be understood as a description of a corresponding block, a corresponding element, an attribute or a functional feature of a corresponding device or a corresponding system.
The following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate example. It should also be noted that although in the claims a dependent claim refers to a particular combination with one or more other claims, other examples may also include a combination of a dependent claim with the subject matter of any other dependent or independent claim. Such combinations are expressly set forth herein unless a specific combination is not intended in an individual case. Furthermore, any other independent claim should also include the features of a claim, even if that claim is not directly defined as being dependent on that other independent claim.
Claims (15)
1. A method (100) for determining a reflectivity value indicative of a reflectivity of an object, the method (100) comprising:
performing (102) a ToF measurement using a time-of-flight ToF sensor, wherein a correlation function of the ToF measurement increases with distance within a measurement range of the ToF sensor such that an output value of the ToF sensor used for the ToF measurement is independent of a distance between the ToF sensor and the object; and
determining (104) the reflectance value based on the output value of the ToF sensor for the ToF measurement.
2. The method (100) of claim 1, wherein the correlation function represents an expected distance-dependent output of the ToF sensor for the ToF measurement, assuming that a light intensity of light received at the ToF sensor during the ToF measurement is constant over distance within the measurement range of the ToF sensor.
3. The method (100) according to claim 1 or claim 2, wherein determining (104) the reflectance value comprises: applying at least one correction to the output value of the ToF sensor for the ToF measurement.
4. The method (100) according to any one of claims 1 to 3, wherein performing (102) the ToF measurement comprises:
illuminating a scene comprising the object with modulated light based on an illumination signal;
driving a light capturing element of the ToF sensor based on a reference signal; and
varying at least one of the illumination signal, the reference signal, and a time offset between the illumination signal and the reference signal during the ToF measurement.
5. The method (100) of claim 4, wherein each of the illumination signal and the reference signal exhibits a respective alternating series of high and low pulses of equal duration, and wherein the time offset between the illumination signal and the reference signal is varied during the ToF measurement.
6. The method (100) according to claim 4, wherein at least one of the illumination signal and the reference signal exhibits a respective alternating series of high-low pulses having different durations, and wherein the respective alternating series of high-low pulses is varied for at least one of the illumination signal and the reference signal during the ToF measurement.
7. The method (100) according to claim 6, wherein the ToF measurement period of the respective alternating series of high and low pulses varies at an increased rate of variation for at least one of the illumination signal and the reference signal.
8. The method (100) according to claim 6 or claim 7, wherein the time offset between the illumination signal and the reference signal is varied during the ToF measurement.
9. The method (100) according to any one of claims 4 to 8, wherein the ToF sensor temporarily exhibits a respective auxiliary correlation function for each variation of the illumination signal, the reference signal and the time offset between the illumination signal and the reference signal used during the ToF measurement, wherein the correlation function of the ToF measurement is a combination of the auxiliary correlation functions, and wherein the at least one of the illumination signal, the reference signal and the time offset between the illumination signal and the reference signal are varied such that the auxiliary correlation functions are offset with respect to each other within the measurement range of the ToF sensor.
10. The method (100) according to any one of claims 4 to 9, wherein the modulated light is emitted by an illumination element of the ToF sensor, and wherein the method (100) further comprises:
measuring a temperature at the lighting element; and/or
Measuring the light intensity and/or the rise time of the modulated light emitted by the lighting element; and
changing at least one of the illumination signal, the reference signal and the time offset between the illumination signal and the reference signal based on at least one of a temperature measured at the illumination element and a measured light intensity and/or rise time of the modulated light emitted by the illumination element.
11. The method (100) according to any one of claims 1 to 10, wherein a course of the correlation function over distance of the ToF measurement depends on an estimated course of an actual light intensity of light received at the ToF sensor over distance within the measurement range.
12. The method (100) according to any one of claims 1 to 11, wherein the correlation function of the ToF measurement is predetermined in a factory calibration.
13. The method (100) according to any one of claims 1 to 12, further comprising:
performing a plurality of ToF calibration measurements to acquire calibration data indicative of the actual light intensity of light received at the ToF sensor for different distances between the ToF sensor and the reference object; and
adjusting the correlation function of the ToF measurement based on the calibration data.
14. The method (100) according to any one of claims 1 to 13, further comprising:
performing one or more additional ToF measurements using the ToF sensor;
determining a distance value indicative of a distance to the object based on an output of the ToF sensor for the one or more further ToF measurements; and
outputting data indicative of the reflectance value and the distance value.
15. An apparatus (200) for determining a value indicative of a reflectivity of an object (201), the apparatus comprising:
a time-of-flight (ToF) sensor (210) configured to perform a ToF measurement, wherein a correlation function of the ToF measurement increases with distance within a measurement range of the ToF sensor (210) such that an output value of the ToF sensor (210) for the ToF measurement is independent of a distance between the ToF sensor (210) and the object (201); and
a processing circuit (240) configured to determine the reflectance value based on the output value of the ToF sensor (210) for the ToF measurement.
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| EP20194844.5A EP3964857A1 (en) | 2020-09-07 | 2020-09-07 | Method and apparatus for determining a reflectivity value indicating a reflectivity of an object |
| EP20194844.5 | 2020-09-07 |
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| EP2477043A1 (en) * | 2011-01-12 | 2012-07-18 | Sony Corporation | 3D time-of-flight camera and method |
| EP2729826B1 (en) * | 2012-01-10 | 2017-04-26 | Softkinetic Sensors N.V. | Improvements in or relating to the processing of time-of-flight signals |
| DE102013207653B4 (en) * | 2012-05-21 | 2018-11-29 | pmdtechnologies ag | Time of flight camera system |
| US9823340B2 (en) * | 2012-12-04 | 2017-11-21 | Texas Instruments Incorporated | Method for time of flight modulation frequency detection and illumination modulation frequency adjustment |
| DE102014115310A1 (en) * | 2014-10-21 | 2016-04-21 | Infineon Technologies Ag | Image forming apparatus and a runtime image forming method |
| US9958383B2 (en) * | 2014-12-18 | 2018-05-01 | Microsoft Technology Licensing, Llc. | Range camera |
| US10230874B2 (en) * | 2015-04-21 | 2019-03-12 | Sony Corporation | Imaging device and imaging control method |
| US9864048B2 (en) * | 2015-05-17 | 2018-01-09 | Microsoft Technology Licensing, Llc. | Gated time of flight camera |
| DE102016219170A1 (en) * | 2015-11-03 | 2017-05-04 | pmdtechnologies ag | Time of flight camera system |
| US11393115B2 (en) * | 2018-11-27 | 2022-07-19 | Infineon Technologies Ag | Filtering continuous-wave time-of-flight measurements, based on coded modulation images |
| DE102018220932A1 (en) * | 2018-12-04 | 2020-06-04 | Osram Gmbh | Method for determining the distance and retroreflectivity of an object surface |
| CN112073708B (en) * | 2020-09-17 | 2022-08-09 | 君恒新信息科技(深圳)有限公司 | Power control method and equipment for TOF camera light emission module |
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| US20220074856A1 (en) | 2022-03-10 |
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